With a sharp rise in olefin price in the petrochemical market, the supply of olefins, particularly light olefins which are used as a raw material for various petrochemical products has become an issue in this market. Among those light olefins, demand for and value of n-butene and 1,3-butadiene which serve as a raw material for various synthetic rubber and copolymer products are increasing currently, especially from China, and methods for producing them include naphtha cracking, direct dehydrogenation of n-butane or n-butene, or oxidative dehydrogenation of n-butane or n-butene. Since approximately 90% of n-butene and 1,3-butadiene supplied to the market are produced by naphtha cracking, the operation of a naphtha cracking process has a great influence in the current market. However, a naphtha cracking process, is for the production of basic petrochemical feedstocks such as ethylene, propylene, etc, not a process dedicated to the production of n-butene and 1,3-butadiene, therefore new establishment or expansion of naphtha cracking center only for the purpose of increasing the production of n-butene and 1,3-butadiene is hardly considered, and if so, it would cause further problems of surplus production of other basic petrochemical feedstocks other than n-butene and 1,3-butadiene. Moreover, with an increasing demand for ethylene and propylene, new establishment and operation regarding a naphtha cracking process tends to be rather focused to increase in production yield of ethylene and propylene, and thus modified as a process using light hydrocarbons such as ethane, propane, etc. as a raw material which can result in high production yield for basic petrochemical feedstock such as ethylene, propylene and the like, although its yield for C4 mixtures is low. In addition to that, with the continuous price increase in raw materials for C4 production, the proportion of a process for obtaining C4 in the naphtha cracking process is relatively reduced. In consequence, with those obstacles as above, it is getting more difficult to secure C4 mixtures, particularly n-butene and 1,3-butadiene through a naphtha cracking process.
As the foregoing description, although n-butene and 1,3-butadiene supply majorly depend on a naphtha cracking process, based on the many reasons as above, the naphtha cracking process cannot be an effective way to resolve the imbalance between supply and demand, caused by recent increased demand in n-butene and 1,3-butadiene. In this circumstance, a dehydrogenation reaction in which hydrogens are removed from n-butane or n-butene thus obtaining n-butene and n-butene, is attracting great attention as an alternative process which can rapidly deal with the current changes in market.
Over the past two decades, although many researches in dehydrogenation of n-butane and n-butene, especially n-butene due to its relatively easy process, have been made and reported [H. H. Kung, M. C. Kung, Adv. Catal., vol. 33, p. 159 (1985); J. A. Toledo, P. Bosch, M. A. Valenzuela, A. Montoya, N. Nava, J. Mol. Catal. A, vol. 125, p. 53 (1997); H. Lee, J. C. Jung, H. Kim, Y.-M. Chung, T. J. Kim, S. J. Lee, S.-H. Oh, Y. S. Kim, I. K. Song, Catal. Lett., vol. 131, p. 344 (2009); H. Lee, J. C. Jung, I. K. Song, Catal. Lett., vol. 133, p. 321 (2009); W. Ueda, K. Asakawa, C.-L. Chen, Y. Moro-oka, T. Ikawa, J. Catal., vol. 101, 360 (1986); R. K. Grasselli, Handbook of Heterogeneous Catalysis, vol. 5, p. 2302 (1997); J. C. Jung, H. Lee, H. Kim, Y.-M. Chung, T. J. Kim, S. J. Lee, S.-H. Oh, Y. S. Kim, I. K. Song, Catal. Lett., vol. 124, p. 262 (2008); J. C. Jung, H. Lee, D. R. Park, J. G. Seo, I. K. Song, Catal. Lett., vol. 131, 401 (2009)], the n-butene price is also sharply rising with rapidly increasing demand from China. Therefore, oxidative dehydrogenation of n-butane is ultimately addressed as an alternative to resolve the current imbalance between n-butene and 1,3-butadiene supply and demand, in petrochemical industry, and thus many related investigations regarding this are being made [N. Kijima, M. Toba, Y. Yoshimura, Catal. Lett., vol. 127, p. 63 (2009); I. C. Marcu, I. Sandulescu, J. M. M. Millet, Appl. Catal. A, vol. 227, p. 309 (2002); L. M. Madeira, J. M. Herrmann, F. G. Freire, M. F. Portela, F. J. Maldonado, Appl. Catal. A, vol. 158, p. 243 (1997); A. A. Lemonidou, G. J. Tjatjopoulos, I. A. Vasalos, Catal. Today, vol. 45, p. 65 (1998)].
The dehydrogenation reaction of n-butane can be classified into direct dehydrogenation and oxidate dehydrogenation, wherein the direct dehydrogenation reaction of n-butane is highly exothermic and thus a thermodynamically disadvantageous reaction since hydrogen should be directly detached from n-butane as well as requires great energy consumption to satisfy the high-temperature reaction condition. For carrying out direct dehydrogenation, used are precious metal catalysts such as platinum or palladium, which require a reactivation process owing to their short lifetime in most cases, therefore the direct dehydrogenation is not a suitable commercial process for producing 1,3-butadiene [A. Wu, C. A. Frake, U.S. Pat. No. 6,433,241 B2 (2002); A. Wu, C. A. Frake, U.S. Pat. No. 6,187,984 (2001)]. On the contrary, unlike the direct dehydrogenation, the oxidative dehydrogenation of n-butane, wherein n-butane and oxygen reacts to produce n-butene and water, and thus obtained n-butene further reacts with oxygen to produce 1,3-butadiene and water, is thermodynamically advantageous since an endothermic reaction turns to an exothermic reaction with the generation of water from the use of oxygen, and rapid temperature changes in catalyst layer which can caused by the heat from the catalyst reaction can be prevented by water generated after the reaction. In this respect, the oxidative dehydrogenation process of n-butane can produce n-butene and 1,3-butadiene through an independent process unlike a naphtha cracking process and be operated under process conditions more advantageous than those of the direct dehydrogenation process. Therefore, when a catalyst process for producing n-butene and 1,3-butadiene with high efficiency is developed, this process can be used as an effective alternative to prior processes to produce n-butene and 1,3-butadiene through an independent energy-saving process.
As described above, the oxidative dehydrogenation of n-butane for producing n-butene and 1,3-butadiene includes a reaction between n-butane and oxygen to produce water and n-butene which reacts with oxygen in the same way again to produce water and 1,3-butadiene. From the above description, although this reaction has many advantages as a commercial process, over the direct dehydrogenation of n-butane in many ways such as a thermodynamic aspect which makes possible to produce n-butene and 1,3-butadiene with a high yield, under mild reaction conditions, it has a drawback that many side reactions such as highly oxidative reactions which involve generation of carbon monoxide or carbon dioxide owing to the use of oxygen as a reactant.
Therefore, the most crucial technical point in the oxidative dehydrogenation process of n-butane is to achieve a catalyst with highly increased selectivity to n-butene and 1,3-butadiene by preventing side reactions such as complete-oxidative reactions, while achieving the conversion of n-butane to the maximum. Although the reaction mechanism of the oxidative dehydrogenation of n-butane has not yet been exactly known, it is reported that, as a first step, solid acid-lattice oxygen cuts the C—H bond of n-butane, which simultaneously causes a redox reaction of a catalyst and loss of lattice oxygen, and therefore complex oxide catalysts containing transition metal ions which may be in various oxidation states are essential to this oxidative dehydrogenation reaction [H. H. Kung, Ind. Eng. Chem. Prod. Res. Dev., vol. 25, p. 171 (1986)].
So far, catalysts known to effectively produce n-butene and 1,3-butadiene through oxidative dehydrogenation of n-butane are magnesium orthovanadate catalysts [M. A. Chaar, D. Partel, H. H. Kung, J. Catal., vol. 105, p. 483 (1987); M. A. Chaar, D. Partel, H. H. Kung, J. Catal., vol. 109, p. 463 (1988); O. S. Owen, H. H. Kung, J. Mol. Catal., vol. 79, p. 265 (1993); A. A. Lemonidou, G. J. Tjatjopoulos, I. A. Vasalos, Catal. Today, vol. 45, p. 65 (1998); Korean patent application No. 10-2011-0021037 (2011) by Song In Kyu, Lee Ho Won, You Yoen Sik, Jo Young Jin, Lee Jin Suck, Jang Ho Sik]; vanadium oxide catalysts [A. F. Dickason, U.S. Pat. No. 3,914,332 (1975); M. E. Harlin, V. M. Niemi, A. O. I. Krause, J. Catal. Vol. 195, p. 67 (2000); V. M. Murgia, E. M. F. Torres, J. C. Gottifredi, E. L. Sham, Appl. Catal. A, vol. 312, p. 134 (2006)]; pyrophosphate catalysts [I. C. Marcu, I. Sandulescu, J. M. M. Millet, Appl. Catal. A, vol. 227, p. 309 (2002); F. Urlan, I. C. Marcu, I. Sandulescu, Catal. Commun., vol. 9, p. 2403 (2008)]; ferrite catalysts [H. Armendariz, J. A. Toledo, G. Aguilar-Rios, M. A. Valenzuela, P. Salas, A. Cabral, H. Jimenez, I. Schifter, J. Mol. Catal., vol. 92, p. 325 (1994); L. Bajars, L. J. Croce, U.S. Pat. No. 3,303,234 (1967)] and the like.
The characteristic feature shared by the above complex oxide catalysts is the presence of transition metals, which are necessary for transition of electrons between the catalyst and n-butane via the redox reaction of the catalyst as explained above [H. H. Kung, Ind. Eng. Chem. Prod. Res. Dev., vol. 25, p. 171 (1986)]. The catalysts can carry out the oxidative dehydrogenation of n-butane by incorporating metals which can be oxidized and reduced such as, for example, vanadium, iron, nickel and titanium, etc, and among them, particularly, magnesium o-vanadate catalysts which contain vanadium are known to have high activity, based on which it is considered for the redox potential of vanadium metal to be suitable for the oxidative dehydrogenation of n-butane [M. A. Chaar, D. Partel, H. H. Kung, J. Catal., vol. 105, p. 483 (1987); M. A. Chaar, D. Partel, H. H. Kung, J. Catal., vol. 109, p. 463 (1988)].
The above-described magnesium o-vanadate catalysts having a chemical formula of Mg3(VO4)2 in a rhombic crystalline form, bind with magnesia in the oxidative dehydrogenation of n-butane to be reduced to, optionally via Mg2VO4 having isometric crystalline structure in the state of vanadium tetraoxide depending on the reaction conditions, MgV2O4 that is in the form of vanadium trioxide and oxygen [N. Kijima, M. Toba, Y. Yoshimura, Catal. Lett., vol. 127, p. 63 (2009)], wherein the reduction process is carried out by receiving electrons generated from the breakage of C—H bond in n-butane. The reduction of the central metal, vanadium ion from pentoxide to trioxide state is the essential element of the oxidative dehydrogenation of n-butane, and the magnesium o-vanadate catalysts can carry out a redox reaction with n-butane via such oxidation state changes of vanadium and thus be served as catalysts for oxidative dehydrogenation to produce n-butene and 1,3-butadiene from n-butane [N. Kijima, M. Toba, Y. Yoshimura, Catal. Lett., vol. 127, p. 63 (2009)].
Magnesium o-vanadate catalysts are generally produced to be the form in which the active phase of Mg3(VO4)2 is supported by a separate metal oxide. It is reported that when magnesium o-vanadate catalysts are not supported, the activity is lower than that of supported magnesium o-vanadate.
For example, some results of oxidative dehydrogenation of n-butane by using unsupported magnesium o-vanadate catalysts have been reported in conventional patents and literatures, specifically, for example, 11.5% of n-butane conversion rate, 6.7% of dehydrogenation product yield under the conditions of 540° C. and the feed composition ratio of n-butane:oxygen:helium=4:8:88[O. S. Owen, H. H. Kung, J. Mol. Catal., vol. 79, p. 265 (1993)], and 5.7% dehydrogenation product yield under the conditions of 540° C. and the feed composition ratio of n-butane:oxygen:helium=5:10:85[A. A. Lemonidou, G. J. Tjatjopoulos, I. A. Vasalos, Catal. Today, vol. 45, p. 65 (1998)]. When magnesium o-vanadate catalysts are supported, the activity can be more improved [A. A. Lemonidou, G. J. Tjatjopoulos, I. A. Vasalos, Catal. Today, vol. 45, p. 65 (1998)]. Specifically, magnesia supported magnesium o-vanadate catalysts obtained by supporting vanadium to excessive amount of magnesia and their excellent activity for the oxidative dehydrogenation of n-butane have been generally reported [M. A. Chaar, D. Partel, H. H. Kung, J. Catal., vol. 109, p. 463 (1988); O. S. Owen, H. H. Kung, J. Mol. Catal., vol. 79, p. 265 (1993); A. A. Lemonidou, G. J. Tjatjopoulos, I. A. Vasalos, Catal. Today, vol. 45, p. 65 (1998)]. Specifically, it was reported that when the oxidative dehydrogenation of n-butane under the conditions of 600° C. and the composition ratio of n-butane:oxygen:nitrogen of 2:1:97 was conducted by using a magnesia-supported magnesium o-vanadate catalyst obtained by mixing magnesium hydroxide with a mixed aqueous solution of ammonium vanadate and ammonia with the ratio of Mg to V of 6:1, it resulted in 30.4% of n-butane conversion rate, 70.6% of dehydrogenation product selectivity and 21.5% of dehydrogenation product yield [N. Kijima, M. Toba, Y. Yoshimura, Catal. Lett., vol. 127, p. 63 (2009)], and when the oxidative dehydrogenation of n-butane under the conditions of 540° C. and the composition ratio of n-butane:oxygen:helium of 5:10:85 was conducted by using a magnesia-supported magnesium o-vanadate catalyst, it resulted in the yield of 22.8% [A. A. Lemonidou, G. J. Tjatjopoulos, I. A. Vasalos, Catal. Today, vol. 45, p. 65 (1998)]. Further, also reported were the results of 35.4% of n-butane conversion rate and 18.1% of dehydrogenation product yield, by using a magnesia-supported magnesium o-vanadate catalyst under the higher oxygen conditions wherein the composition ratio of n-butane:oxygen:helium=5:20:75, as compared to said reactions of the prior arts [J. M. Lopez Nieto, A. Dejoz, M. J. Vazquez, W. O'Leary, J. Cunnungham, Catal. Today, vol. 40, p. 215 (1998)].
Further reported was a method for using magnesium o-vanadate catalyst which makes possible to increase the activity for the oxidative dehydrogenation of n-butane by mixing additives to magnesia-supported magnesium o-vanadate catalyst so as to obtain products from the dehydrogenation, n-butene and 1,3-butadiene with high yield in the literature of [D. Bhattacharyya, S. K. Bej, M. S. Rao, Appl. Catal. A, vol. 87, p. 29 (1992)], wherein the dehydrogenation was carried out under the conditions of 570° C., a composition ratio of n-butane:oxygen:nitrogen of 4:8:88 by using 25 wt % of a magnesia-supported magnesium o-vanadate catalyst further mixed with titanium oxide and chromium oxide, resulting in 54.0% of n-butane conversion rate and 33.8% of dehydrogenation product yield.
Although it is possible to the desired reaction product n-butene and 1,3-butadiene with a very high yield, by using said magnesia-supported magnesium o-vanadate catalyst in the oxidative dehydrogenation of n-butane, its commercial application is limited. This is because that although the magnesia-supported magnesium o-vanadate catalyst has high activity, the redox reaction of the catalyst which should be reversible is carried out partly irreversible, [N. Kijima, M. Toba, Y. Yoshimura, Catal. Lett., vol. 127, p. 63 (2009)], resulting in the high catalyst activity is not maintained for a long time.
Therefore, there are needs for development of novel catalysts which can maintain the catalyst activity for an extended period without loss of initial catalyst activity.